Abstract:

A case study examining the relationship between stream temperatures
and the thermal environment through which streams flow was conducted on the
headwaters of 4 tributaries of the Burnt River (Barney, Elk, Greenhorn, and Stevens
Creeks) in northeastern Oregon during July through August 1998 and 1999. Barney
Creek and Stevens Creek are in adjacent drainages, both with northerly aspects. Barney
Creek drainage was completely burned over in 1989 while Stevens Creek vegetation
remained intact. Elk Creek had 2 cold water tributaries and groundwater inputs.
Greenhorn Creek was much more variable in terms of disturbance and vegetation.
Stream discharge and air, soil, and water temperature data were collected at 150
m increments from 1370 to 1830 m elevation on each stream. Analyses compared daily
mean air, soil, and water temperatures at each elevation within each stream, year, and
month. Mean daily minimum and daily maximum air and water temperatures were also
analyzed. For all streams in this study. elevation was significantly associated with air,
soil, and water temperatures (p<O.000I). For most cases on each of the streams, mean
daily air, soil, and water temperatures increased with every 150 meter drop in elevation. The thermal environment (air and soil surrounding the stream) as well as the stream
temperatures responded similarly on each creek. Barney Creek had the overall highest
mean daily air, soil, and water temperatures, followed by Greenhorn, Stevens, and Elk
Creeks. Barney Creek was burned over in 1989 and had essentially no overstory
canopy cover. Elk Creek consistently had the lowest mean daily air, soil and water
temperatures. Elk Creek received substantial cold water subsurface and from 2
tributaries. Of the 4 creeks, Stevens Creek consistently had the greatest increases in
mean daily air, water, and soil temperatures with descending elevation. Stevens Creek
was adjacent to and very similar to Barney Creek with 2 notable differences. Stevens
Creek had intact forest overstory canopy and it carried about half the flow of Barney
Creek. Greenhorn Creek was the most variable in terms of temperature changes with
descending elevation for mean daily air, water, and soil. Greenhorn Creek has been
heavily disturbed by mining activity.
Elevation was also significant for mean daily maximum temperatures for air,
soil, and water (p<O.000I). Mean daily maximum air and water, as well as mean daily
minimum water temperatures generally increased with descending elevation on all 4
streams. Mean daily minimum air temperature showed more variation with elevation,
and likely reflected patterns of cold air drainage or cold air pockets. Thermal
environment, heavily influenced by elevation, appeared to be a major influence on
stream temperature.